AMP deaminase (AMPD; EC 3.5.4.6) is a diverse and highly regulated enzyme located at a branchpoint in the adenylate catabolic pathway. AMPD plays a key role during metabolic imbalances of energy supply and demand homeostasis by competing with 5' nucleotidase for available AMP. This role is underscored in striated muscle where inheritance of a prolonged survival in congestive hart failure. These opposing clinical consequences reflect a functional difference in adenylate catabolism in various striated muscles due, in part, to distinct regulatory features of AMPD isoforms. Emerging data show that divergent N-terminal domains in AMPD polypeptides alter physical and functional properties of the enzyme. The long-term objective of this project is to gain a comprehensive understanding of AMPD regulation in striated muscle with an emphasis on the functional significance for divergent N-terminal domains. The continued pursuit of this goal will be accomplished by expressing, isolating an characterizing wild type and genetically modified human AMPD recombinant enzymes that will be used to 1) define the structural bases and functional effects of phosphorylation and phosphoinositides on the catalytic and actomyosin binding properties of human AMPD recombinant isoforms. These analyses will also sere to assess the relationship between these two opposing regulators of AMPD catalytic activity, 2) determine the combined effects of a cassette-type alternative splicing event and a P43L substitution on the human AMPD1 recombinant enzyme. This latter information is central to hypotheses designed to explain clinical outcomes resulting from inheritance of the prevalent AMPD1 mutant allele, and 3) attempt to solve the crystal structure of the human AMPD1 recombinant enzyme. Detailed structural knowledge of AMPD1 will facilitate our understanding of the complex regulation of this enzyme. These combined efforts should provide critical information that may help explain clinical outcomes associated with a prevalent AMPD1 mutant allele.